This invention relates to grease guns and more specifically to a grease gun of exceptional strength and use convenience which is formed of a polymeric material.
A grease gun is a device of injecting grease under pressure into a bearing cavity through a fitting such as a grease nipple. Conventional grease guns have been essentially unchanged for years and are widely regarded as being entirely adequate in their present design. However, I have ascertained several aspects of the conventional grease gun which I believe is susceptible of substantial improvement.
The conventional grease gun barrel is a cylindrical steel tube threaded at each end. The tube is sometimes knurled to improve the grip on the barrel and is stamped or inscribed with the name of the manufacturer or the OEM distributor, and then is painted for appearance and rust protection. Likewise, the pump lever which is linked to the head cap of the grease gun is a steel member drilled to receive the pins which connect it to the head cap and also to the pump piston and is painted for appearance and rust protection.
Finally, the end cap is a steel member internally threaded to be threaded onto the end of the barrel and painted like the barrel and the handle for appearance and rust protection.
Although many of the operations required to produce these parts are formed by automated operations, the cost is relatively high compared to, for example, plastic molding operations. Moreover, the steel members are heavy and can become tiring to a mechanic or service person who must work overhead or in cramped positions to reach the grease fittings on the machinery on which he is working. The steel barrel often becomes coated with grease in use and can become slippery which, combined with its heavy weight, increases the likelihood that it will slip from the hands of the service person and fall onto equipment or other persons with consequent damage. Moreover, the rough handling that a grease gun often receives invariably results in the paint coating becoming chipped and scratched which defeats the rust prevention purpose and also detracts from its appearance, with consequent adverse affect on the image or good name of the manufacturer or OEM supplier.
One further problem with steel grease gun parts is that they are thermally and electrically conductive. In the winter when the temperature is very cold, the steel barrel of a conventional grease gun can be very uncomfortable to hold because it feels so cold to the skin. In addition, in certain locations in which grease guns are commonly used, such as farms and equipment leasing operations, it is not uncommon for electrical wiring to be exposed and susceptible to contact by a grease gun in the hands of a service person. An electrically insulated grease gun would not expose the service person to this danger.
It occurred to me that use of plastic parts in a grease gun would eliminate many of the disadvantages noted above. However, most plastic materials have properties which would make them unsuitable for use as substitute materials in the conventional grease gun parts. This may explain the absence of plastic grease guns on the market. One such property is a decrease in impact resistance at low temperature. Since a grease gun is often used in cold temperatures and is frequently dropped, sometimes from considerable heights, a low impact resistance would be a severe drawback to the use of plastic parts in a grease gun. In addition, the threading of plastic parts decreases their strength because of the notch effect of the threads in the plastic which creates a stress concentration which leads to formation of a crack which then propagates through the plastic quickly and causes a complete fracture of the plastic part. Finally, plastic threads can easily become cross-threaded unless care is taken to thread it properly and cross-threading can permanently damage the threaded end of the plastic part. This would cause misalignment between the barrel and the head cap which could prevent the grease seal from functioning properly at that location and therefore cause leakage of grease. Finally, the automatic unthreading of a plastic part from the mold requires the use of an expensive machine which would decrease the cost savings which the use of plastic parts would achieve.